This application claims priority of U.K. Patent Application No. GB 0105547.7, filed Mar. 7, 2001, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a tool holder for a rotary hammer or chisel hammer.
2. Description of the Related Art
Different types of tool holder are known which have a main body with, extending rearwards from the front end thereof, a receiving opening for the shank of a drill bit or chisel of the type having at least one axial groove closed at both ends. The main body is formed with at least one axially extending elongate through-opening in the wall of the main body. A locking element of smaller axial length than the through-opening is inserted in the through-opening. The locking element in a locked position is supported against outward radial displacement and, when the drill bit or chisel is inserted, engages in the at least one axial groove thereof. The locking element in a released position is displaceable radially outwards relative to the locked position. A forwardly biased supporting ring is provided on the main body, which is axially movable between a position supporting the locking element in the locked position and a second position defining the released position of the locking element. The tool holder also has an adjusting sleeve, which is axially movable to move the supporting ring between positions.
It should be mentioned that, in addition to the at least one axial groove closed at both ends, the drill bits insertable in such a tool holder generally have at least one further axial groove offset through 90xc2x0 with respect to the axial groove, which further groove is open at the rear end of the drill bit and in the inserted state of the drill bit is engaged by an axial rib of the main body, by means of which the torque for rotation of the drill bit is transferred to the drill bit. Such drill bits are known, for example, as so-called SDS-Plus and SDS-Max drill bits. Since no rotary forces are transferred to chisels that are used in a chisel hammer, the shank of such a chisel often does not have an axial groove open at the rear end, but only one or two axial grooves closed at both ends, in which the locking element or elements engage to hold the chisel fixedly in the tool holder so that it has limited axial displacement.
In a known tool holder of the above-mentioned kind (EP 0 668 127 A1), there are two diametrically opposite elongate through-openings in the main body, and inserted in each of these through-openings is a locking element in the form of a cylindrical roller. In the locked position the cylindrical roller is located at the front end of the through-opening and is supported by a supporting ring against radial outward displacement. To secure this front position of the locking elements, a divided supporting plate is provided, which engages with finger-like radially inwardly directed extensions into the through-openings and is pressed by a spring into a front position, which is defined by the front or locked position of the supporting ring. By pushing back an adjusting sleeve, the supporting ring is displaced axially rearwards as far as the rear end of the locking elements into its second position. In the region in front of the supporting ring, the adjusting sleeve has an inner wall lying radially further outwards than the inner surface of the adjusting sleeve, so that the locking elements are then able to yield radially outwards into that region of the adjusting sleeve, in order to disengage from the axial grooves in the shank of the inserted drill bit or chisel and release the latter.
If a drill bit or chisel is inserted into this tool holder, then the rear end of its shank comes into contact with the front ends of the locking elements, and these are brought into engagement with the finger-like extensions of the disc projecting into the through-openings of the main body and together with the disc are displaced rearwards against spring force until they are able to yield radially outwards behind the supporting ring located in the locked position, so that the shank can be introduced further into the receiving opening until the locking elements enter its axial grooves and, as a result of the spring force acting on the supporting disc, are again moved forwards into their starting position. In that position, they are then supported by the supporting ring against outward radial displacement.
This tool holder works satisfactorily and combines a compact construction with simple assembly. But because the forces acting on the locking elements and the surrounding parts increase with heavier-duty rotary hammers and chisel hammers, the diameter and/or the length of the cylindrically shaped locking elements has to be correspondingly increased. This leads to an increase in the breadth and/or axial length of the through-openings of the main body, however, and hence to substantial material weakening. Extending the locking element moreover requires a greater axial travel of the supporting ring for displacement into its second position and also a greater axial travel of the locking element for displacement into the position in which it is able to yield radially outwards, and consequently an increase in the overall axial length of the tool holder.
It is furthermore already well known to use, instead of cylindrically shaped locking elements, shaped elements that in the locking position project beyond the periphery of the outer wall of the circumference of the main body, and which cooperate both with a radially stepped supporting ring and with a positioning ring, the positioning ring engaging by means of a finger portion in a radially outwardly open recess in the locking element. The positioning ring is spring-loaded in the forward direction and therefore presses forwards the locking element and the adjusting sleeve that is present, so that the locking element is positioned in a region of the supporting ring which supports the locking element against radially outward displacement. If the adjusting sleeve is displaced axially rearwards by the user, then the positioning ring is also displaced rearwards, and on being displaced the finger portion of the positioning ring takes the locking element with it. The locking element therefore enters a position in relation to the supporting ring in which the locking element can be displaced radially outwards, so that the inserted drill bit or chisel can be withdrawn from the receiving opening of the main body.
When a drill bit or chisel is inserted into this known tool holder, the locking elements are displaced axially rearwards by abutment of the rear end of the drill bit or chisel against the front end of the locking elements, and hence the positioning ring too is pushed rearwards against the force of the forwardly acting spring until the locking elements have reached the above-mentioned position in which they are able to yield radially outwards in the region of the supporting ring. The rear end of the drill bit or chisel then slides past the locking elements, and the spring-loaded positioning ring displaces the locking elements axially forwards into the through-openings of the main body, so that they enter the axial grooves of the shank of the drill bit or chisel and take up the position in which the supporting ring supports them against radially outward displacement.
This known construction allows the use of compact locking elements of greater strength than the roll-shaped locking elements, but, in addition to the use of a supporting ring, requires the use of a positioning ring, by means of which displacement of the locking elements is effected by movement of the adjusting sleeve. Moreover, the external shape of the locking elements is comparatively complicated, so that a complicated mould is required for manufacture, if this involves sintering, for example.
In a further known tool holder design disclosed in GB2,338,672 the tool holder is constructed with locking elements consisting of a shaped element which, on its radially outermost side, has a recess lying between two axially spaced projections, the supporting ring has on its inside two recesses lying between three axially spaced projections, the shape of the projections of the supporting ring being matched to the shape of the recess in the locking element and the shape of the projections of the locking element being matched to the shape of the recesses in the supporting ring. In the locking position of the locking element the projections thereof abut the projections of the supporting ring and, in the second position of the supporting ring, a projection of the locking element is received in one of the recesses in the supporting ring. As a drill bit or chisel is inserted into the receiving opening, the locking element is displaced by the rear end of the drill bit or chisel rearwards against spring force into a second release position, in which the front projection of the locking element engages in the front recess in the supporting ring and the rear two projections of the supporting ring engage in the recess in the locking element. The release position is reached after an axial displacement movement that is substantially shorter than the axial length of the supporting ring. The principle advantage of this design of tool holder is that the length through which the supporting ring or the locking element must travel between the first and second positions is reduced, which can enable the tool holder to be more compact. However, the complex shape of the supporting ring and the locking elements can increase manufacturing costs. Furthermore, the locking elements are relatively long and require through holes that are longer than the locking elements, which can weaken the main body of the tool holder, which must withstand repeated heavy impacts.
The object of the invention is to produce a tool holder of the simplest possible construction and of short overall length, which is also suitable for use in high-performance rotary hammers and chisel hammers.
According to the present invention there is provided a tool holder for a rotary hammer or chisel hammer, having a main body with a receiving opening for the shank of a drill bit or chisel having at least one axial groove closed at both ends, at least one axially extending, elongate through-opening in the wall of the main body, inserted in the through-opening a locking element of smaller axial length than the through-opening, which locking element in a locked position is supported against outward radial displacement and when the drill bit or chisel is inserted, engages in the at least one axial groove thereof and, which in a release position is displaceable radially outwards relative to the locked position, and a supporting ring is axially movable between a position supporting the locking element in the locked position and a second position defining a first release position of the locking element, characterised in that the locking element consists of a shaped element which, on its radially outer side, has a single projection lying between a first recess formed at the front edge of the locking element and a second recess formed at the rear edge of the locking element, the supporting ring has on its radially inner side a single projection lying between a first recess formed at the front edge at the supporting ring and a second recess formed at the rear edge of the supporting ring, wherein the shape of the projection of the supporting ring matches the shape of the recesses in the locking element and the shape of the projection of the locking element matches the shape of the recess in the supporting ring, and in that in the locking position of the locking element the projection thereof abuts the projection of the supporting ring and, in a release position of the locking element, part of the projection of the locking element is received in one of the recesses of the supporting ring.
The locking elements and supporting ring according to the present invention are of relatively simple shape and so are accordingly relatively cheap and simple to manufacture. The locking elements are also relatively short. Furthermore, the locking elements do not have to be moved all the way past the supporting ring, or vice versa, to move into their unlocked position. This means that the through-openings in the tool holder can be relatively short and so do not unduly weaken the main body, and that the locking elements and/or the supporting ring only have to be moved a short axial distance between the locked and unlocked positions.
The tool holder may additionally include a manually actuable adjusting sleeve, which may surround the supporting ring, and which as axially moveable to move the supporting ring between positions. Preferably a spring loads the supporting ring towards its position supporting the locking element in the locked position. This ensures that the supporting ring returns to its locked position automatically after is has been moved to its second position.
In the first release position of the locking element, when the supporting ring is in its second position, it is preferred that part of the rear of the projection of the locking element is received in the first recess of at the front of the supporting ring.
In a preferred version of the tool holder into which a drill bit or chisel can be fitted without moving the supporting ring, as a drill bit or chisel is inserted into the receiving opening, the or each locking element is displaced by the rear end of the drill bit or chisel rearwards against spring force into a release position, in which a forward part of the projection of the locking element engages in the second recess at the rear edge of the supporting ring and the rearward part of the projection of the supporting ring engages in the first recess at the front edge of the locking element. In this way, the locking element is well supported in its unlocked position.
Preferably, an outer spring loads the supporting ring towards its position in which it supports the locking element in the locked position. Accordingly, when the supporting ring is moved to its second release position and a drill bit or chisel is removed, the adjusting sleeve can be released to move the supporting ring and locking element back to their locked positions (with no drill bit or chisel fitted).
To improve guidance of the locking elements between their locked and unlocked positions on insertion of a drill bit or chisel, a forwardly biased washer, which in the locked position abuts the rear end of the locking element, and in the second release position the washer is displaced rearwards together with the locking element. For improved guidance of the locking element between its locked and second release position, the washer may have an inwardly facing shoulder on its forward face which engages the rearward edge of the second recess of the locking element. The washer may also abut the rear end of the supporting ring and in the first release position the washer may be displaced rearwards together with the supporting ring. The washer may be forwardly biased by an inner spring located inwardly of the spring referred to above for forwardly biasing the supporting ring.
In order to provide adequate damping of the impact to the locking elements on entry into idle mode of the hammer, the locking element is preferably supported in the locked position with its front end against a resiliently deformable support.
The inserted locking element is preferably symmetrically shaped both with respect to an axial plane extending through the centre of the locking element and with respect to a radial plane extending through the centre of the locking element. This means that the locking element cannot be assembled in an incorrect orientation within the through-openings. For the same reason it is preferred that the supporting ring is symmetrically shaped with respect to a radial plane extending through the centre of the supporting ring. In particular the projection of the supporting ring may be in the form of an annular rib.
In a preferred embodiment of the present invention, the projection of the locking element is of trapezoidal cross-section in axial section and tapers radially outwards in this sectional plane, and the projection of the supporting ring is of trapezoidal cross-section in axial section and tapers radially inwards in this sectional plane at the same slope as the projection of the locking element. This with provide smooth transitions between the relative positions between the locking element and the supporting ring.
In an especially preferred embodiment there are two locking elements, each of which are received in one of two through-openings in the main body.
According to a second aspect of the present invention there is provided a rotary or chisel hammer comprising a tool holder as described above.